Ferromagnetic material for gyromagnetic effect



April 1961 c. L. GUILLAUD ETAL 2,980,618

FERROMAGNETIC MATERIAL FOR GYROMAGNETIC EFFECT Filed May 1, 1957 Alfenual/on in dec/be/s ZO'O 0 25 5 /0 /5 2 Inventor (LL. Grumuu RNaukiar Bylmw w A Home y United.

FERROMAGNETIC MATERIAL FOR GYROMAGNETIC EFFECT Charles Louis Guillaud and Roger Vautier, Bellevue, France, assignors to Centre National de la Recherche Scientifique, Paris, France, a French government administration The present invention relates to ferromagnetic ceramic material intended for use in devices in which the gyromagnetic effect at hyperfrequencies is required.

These devices may be, in particular, switches, phase shifters, modulators, routing devices, separators, that is to say, devices having diflerent attenuations in the two directions of transmission of the electromagnetic wave, the above list not being of a limitative nature.

For the purpose of comparison the properties of the materials will be considered in the particular case of a device making use of the Faraday effect in which a cylindrical rod, of circular cross-section is placed in the axis of a wave guide of circular cross-section and subjected to a steady longitudinal magnetic field. The circular wave-guide is connected at each end by suitable transition sections to lengths of rectangular waveguide. An electromagnetic wave is propagated in one of the rectangular wave guides in the TE mode, in which the electric vector is parallel to the short side of the guides. This mode is converted in the circular wave guide to the TE mode, and this mode is again converted to the TE mode in the succeeding section of rectangular waveguide.

The effect of the presence of the ferromagnetic ceramic material subjected to a longitudinal magnetic field is to rgtat e the direction of polarisation of the electromagnetic wave through an angle which is dependent upon the magnetic field within the material, upon the composition of the material and upon the length and the diameter of the rod. The rectangular. wave guides are disposed at an angle with respect to one another dependent upon the angle through which the plane of polarisation of the electromagnetic waves is to be rotated. The plane of polarisation is rotated in the same direction for both directions of transmission so that waves proceeding from one rectangular wave guide to the other have the plane of polarisation rotated for transmission along the last mentioned wave guide whereas waves proceeding in the reverse direction have the plane of polarisation rotated so that the waves are little or not at all, propagated into the first mentioned wave guide.

In addition to a rotation of the plane of polarisation an electromagnetic wave traversing such a device as described above suffers some attenuation and the efiiciency of the device may be measured by the ratio Angular rotation of plane of polarisation Attenuation for a given length of rod of ferromagnetic ceramic materials.

According to the present invention the efiiciency of a rod of ferromagnetic ceramic material comprising a nickel zinc ferrite having a nickel oxide content between 13 mol percent and 20 mol percent is increased in a device utilising the gyromagnetic effect by incorporating therein between 2 and 20 molar percent of chromic oxide (Cr O The remaining materialmay consist of between 30 and 50 mol percent of ferric oxide with the rest being zinc oxide.

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Patented Apr. 18, 196i I "ice The invention will be better understood from the following description taken in conjunction with the accompanying drawings in which Fig. 1 shows the efiect of different percentage additions of chromic oxide on the angle of rotation of plane of polarisation, and

Fig. 2 shows the effect of different percentage additions of chrornic oxide on the attenuation.

Referring to the drawings Fig. l is a curve showing the rotations of the plane of polarisation of rods of the same dimensions but of different ferromagnetic ceramic materials. The basic material is a nickel zinc ferrite containing 18 mol percent of NiO, 32 mol percent of ZnO, 50 mol percent of Fe O To different batches of this material were added different molar percentages of chromic oxide, in place of an equivalent percentage of Fe O shown as abscissae. The angles of rotation of the plane of polarisation for electromagnetic waves of frequency 10,000 mc./s. are given as ordinates. It will be observed that the angle of rotation decreases as the amount of chrornic oxide increases.

Fig. 2 is a curve showing the attenuation in decibels (as ordinates) for the same materials as in Fig. 1 and it will be noted that the attenuation decreases with increasing content of chromic oxide. The eificiency as measured by rotation, per decibel of attenuation is increased by the addition of up to 20 mol percent Cr O Ceramic materials according to the invention may contain between 46 and 54 mol percent of the sum of chromic oxide and ferric oxide, of which between 2 mol percent and 15 mol percent is chromic oxide, between 13 and 20 mol percent of nickel oxide and the remainder Zinc oxide.

The particular percentage of chromic oxide to be used depends upon the nickel oxide content. The shapes of curves such as those in Figs. 1 and 2 are generally the same for all materials according to the invention but vary slightly according to the nickel oxide content. The presence of chromic oxide has some effect upon the temperature of heat treatment of the mixture of oxides required to attain a given intensity of magnetic saturation in the material. In general the molecular content of chromic oxide is chosen to realise the test compromise amongst the desired properties for a particular application.

In the following examples the gyromagnetic properties of materials according to the invention are defined in a device such as described above making use of the Faraday effect because the results of measurements in such a device are most characteristic of the material, but it is to be understood that materials according to the present invention are of use in any device which makes use of gyromagnetic properties.

In the following examples, measurements are also given for the ellipticity of the wave emerging from the circular wave guide. This ellipticity is measured in decibels by the logarithm of the ratio of the maximum power to the minimum power and in the experiments to which the results relate the output rectangular guide was rotated about its axis to determine this ratio.

Example 1.In a ball mill, of iron, a mixture of the following constituents is ground for 24 hours in the molecular proportions indicated: NiO, 18%; Cr O 10%; Fe O 41%; Zoo, 31%. This product, after pressing, is sintered at a temperature of 1250 C. for four hours in an oxygen atmosphere, and then cooled for 16 hours in the same atmosphere. A material of this kind, employed in the form of a circular cylindrical bar 5.5 mm. in diameter and 30 mm. long, produces at the frequency of 9,700 mc./s. a rotation of 30 when it is subjected to a longitudinal magnetic field equal to oersted. The attenuation of the wave is 0.04 decibel. The ellipticity of the emerging wave measured, as explained above, is higher than 30 decibels,

By-way of comparison,--a material prepared and employed .under. the...same..conditions, but with the following molecular percentages: NiO, 18%; Fe O 51%; ZnO, 31%; produces a rotation of 65 and an attenuation of 0.7 decibel.

Example 2.--A mixture ofthefollowing composition is ground in the molecular proportions indicated: NiO, 18%; Cr O Fe O 40%; ZnO, 32%. This product, after pressing, is sintered at a temperature of 1250 C. for four hours in an oxygen atmosphere. A material of this kind, employed in the form of a circular cylindrical bar 6 mm. in diameter'and 30mm. long, produces at the frequency of 9,700 mc./s. a rotation of 48 when it is subjected to a longitudinal magnetic field equal to 100 oersted. The attenuation of the wave is 0.08 decibel.

By way of comparison a material prepared and employed under the same conditions but with the molecular percentages: NiO, 18%; Fe O 50%; ZnO, 32%; produces a rotation of 70 and an attenuation of 0.8 decibel.

Example 3.-The following mixture is ground in the molecular proportions indicated: NiO, 18%; Cr O Fe O 35%; ZnO, 32%. This product, after pressing, is sintered at a temperature of 1200 C. for four hours in an oxygen atmosphere. This material, used in the form of a circular cylindrical bar 5.5 mm. in diameter and 30 mm. long, produces at the frequency of 9,700 mc./s. a rotation of 45 and anattenuation of 0.05 decibel, when subjected to a longitudinal magnetic field equal to 100 orsted.

Example 4.The following mixture is ground in the molecular proportions indicated: NiO, 17%, Cr O 7%; Fe O 44%; ZnO, 32%. After pressing and sintering at a temperature of 1200 C. for fourhours in an oxygen atmosphere, this material, used-in the form of a circular cylindrical bar 5.5 mm. in diameter and 30 mm. long, produces at a frequency of 9,700 mc./s. a rotation of 30 and a negligible attenuation, when subjected to a longitudinal magnetic field of 100 oersted.

Example 5.-The following mixture in molecular percentage: NiO, 17%; Cr O 7%; Fe O 44%; ZnO, 32%; is ground, then pressed. It is then sintered at 1200" C. for four hours in an oxygen atmosphere. Used in the form of a circular cylindrical bar 6.5 mm. in diameter and 30 mm. long, this material, subjected to a longitudinal magnetic field of 100 oersted, produces a rotation of 90 and an attenuation of 0.3 decibel.

Example 6.'The following mixture in molecular percentage NiO, 13%; Cr O 5%; Fegog, 49%; ZnO, 33% is ground, pressed and sintered at 1250 C. for 4 hours in an oxygen atmosphere. Used in the form of a circular cylindrical bar 5.3 mm. in diameter and 30 mm. long, this material produces a rotation of 50 for a Wave of 9700 mc./s. an attenuation of 0.17 db and an ellipticity of the emerging wave greater than 35 db when subjected to a longitudinal magnetic field of 100 oersted.

Example 7.A composition in molecular percentages of NiO, Cr O 20%; Fe O 30%; Z110, 30% sintered for 4 hours at 1200 C. in an oxygen atmosphere and in the form of a circular rod of 6.5 mm. diameter and 30 mm. long gave, at 9700 mc./s. a rotation of an attenuation of 0.09 db and an ellipticity greater than 35 db when subjected to a longitudinal magnetic field of 100 oersted.

Itrcan be seen from the data given above that the attenuation decreases more rapidly than doesthe rotation of the angle of polarisation within the limits of chromic oxide content indicated and this fact may .be used in the:

selection of the particular composition to be used. The

molecular content of chromic oxide may however be chosen to realise the best compromise the particular device contemplated, since theiinvention is not limited to devices of the particular kind described.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the in- 'vention.

What we claim is:

1. A body of ferromagnetic ceramic material having the properties of a large angle of rotation of the plane of polarisation for energy of microwave frequencies when placed in a longitudinal magnetic field and presenting a low attenuation to said frequencies, said body being the reaction product of a finely divided mixture of from 13 to 20 mol. percent of nickel oxide, from 5 to 20 mol. percent of chromic oxide, from 30 to mol. percent of ferric oxide and the remainder zinc oxide, the sum of the chromic oxide and the ferric oxide comprising between 46 and 54 mol. percent of the material, said mixture being compressed and sintered at a temperature between approximately 1200 C. and approximately 1250 C. in an oxygen atmosphere for approximately four hours.

2. A body of ferromagnetic ceramic material having the properties of a large angle of rotation of the plane of polarisation for energy of microwave frequencies when placed in a longitudinal magnetic field and'presenting a low attenuation to said frequencies, said body being the reaction product of a finely divided mixture of from 13 to 20 mol. percent of nickel oxide, from 10 to 20 mol. percent of chromic oxide, from 30 to 50 mol. percent of ferric oxide and the remainder zinc oxide, the sum of the chromic oxide and the ferric oxide comprising between 46 and 54 mol. percent of'the material, said mixture being compressed and sintered at a temperature between approximately 1200 C. and approximately 1250 C. in an oxygen atmosphere for approximately four hours.

3. A body of ferrogamnetic ceramic material having the properties of a large angle of rotation of the plane of polarisation for energy of microwave frequencies when placed in a longitudinal magnetic field and presenting a low attenuation to said frequencies, said body being the. reaction product of a finely divided mixture of from 13 to 20 mol. percent of nickel oxide, from 5 to 15 mol. percent of chromic oxide, from 35 to 49 mol. percent of ferric oxide and the remainder zinc oxide, the sum of the L chromic oxide and the ferric oxide comprising between 46 and 54 mol. percent of the material, said mixture being compressed and sinteredat a temperature between approximately 1200 C. and approximately 1250 C. in an oxygen a mosphere for approximately four hours:

Referenc s Cited in the file of this patent UNITED STATES PATENTS I 2,579,267 Leverenz Dec. 18, 1951 2,579,978 Snoek et a1. Dec..25, 1951 FOREIGN PATENTS 524,097 Belgium Nov. 30, 1953 1,074,864 France Apr. 7, 1954 1,107,654 France Aug. 10, 1955 OTHER REFERENCES Harvey et al.: R.C.A. Review, vol. XI, No. 3, pages 349, 361, September 1950, pub. by R.C.A., Princeton, NJ. 

1. A BODY OF FERROMAGNETIC CERAMIC MATERIAL HAVING THE PROPERTIES OF A LARGE ANGLE OF ROTATION OF THE PLANE OF POLARISATION FOR ENERGY OF MICROWAVE FREQUENCIES WHEN PLACED IN A LONGITUDINAL MAGNETIC FIELD AND PRESENTING A LOW ATTENUATION TO SAID FREQUENCIES, SAID BODY BEING THE REACTION PRODUCT OF A FINELY DIVIDED MIXTURE OF FROM 13 TO 20 MOL. PERCENT OF NICKEL OXIDE, FROM 5 TO 20 MOL. PERCENT OF CHROMIC OXIDE, FROM 30 TO 50 MOL. PERCENT OF FERRIC OXIDE AND THER REMAINDER ZINC OXIDE, THE SUM OF THE CHROMIC OXIDE AND THE FERRIC OXIDE COMPRISING BETWEEN 46 AND 54 MOL. PERCENT OF THE MATERIAL, SAID MIXTURE BEING COMPRESSED AND SINTERED AT A TEMPERATURE BETWEEN APPROXIMATELY 1200*C. AND APPROXIMATELY 1250*C. IN AN OXYGEN ATMOSPHERE FOR APPROXIMATELY FOUR HOURS. 